/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec.compression;

/**
 * A 256 entry Move To Front transform.
 */
final class Bzip2MoveToFrontTable
{
    /**
     * The Move To Front list.
     */
    private final byte[] mtf =
    { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
            21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37,
            38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54,
            55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71,
            72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88,
            89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104,
            105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117,
            118, 119, 120, 121, 122, 123, 124, 125, 126, 127, (byte) 128,
            (byte) 129, (byte) 130, (byte) 131, (byte) 132, (byte) 133,
            (byte) 134, (byte) 135, (byte) 136, (byte) 137, (byte) 138,
            (byte) 139, (byte) 140, (byte) 141, (byte) 142, (byte) 143,
            (byte) 144, (byte) 145, (byte) 146, (byte) 147, (byte) 148,
            (byte) 149, (byte) 150, (byte) 151, (byte) 152, (byte) 153,
            (byte) 154, (byte) 155, (byte) 156, (byte) 157, (byte) 158,
            (byte) 159, (byte) 160, (byte) 161, (byte) 162, (byte) 163,
            (byte) 164, (byte) 165, (byte) 166, (byte) 167, (byte) 168,
            (byte) 169, (byte) 170, (byte) 171, (byte) 172, (byte) 173,
            (byte) 174, (byte) 175, (byte) 176, (byte) 177, (byte) 178,
            (byte) 179, (byte) 180, (byte) 181, (byte) 182, (byte) 183,
            (byte) 184, (byte) 185, (byte) 186, (byte) 187, (byte) 188,
            (byte) 189, (byte) 190, (byte) 191, (byte) 192, (byte) 193,
            (byte) 194, (byte) 195, (byte) 196, (byte) 197, (byte) 198,
            (byte) 199, (byte) 200, (byte) 201, (byte) 202, (byte) 203,
            (byte) 204, (byte) 205, (byte) 206, (byte) 207, (byte) 208,
            (byte) 209, (byte) 210, (byte) 211, (byte) 212, (byte) 213,
            (byte) 214, (byte) 215, (byte) 216, (byte) 217, (byte) 218,
            (byte) 219, (byte) 220, (byte) 221, (byte) 222, (byte) 223,
            (byte) 224, (byte) 225, (byte) 226, (byte) 227, (byte) 228,
            (byte) 229, (byte) 230, (byte) 231, (byte) 232, (byte) 233,
            (byte) 234, (byte) 235, (byte) 236, (byte) 237, (byte) 238,
            (byte) 239, (byte) 240, (byte) 241, (byte) 242, (byte) 243,
            (byte) 244, (byte) 245, (byte) 246, (byte) 247, (byte) 248,
            (byte) 249, (byte) 250, (byte) 251, (byte) 252, (byte) 253,
            (byte) 254, (byte) 255 };

    /**
     * Moves a value to the head of the MTF list (forward Move To Front
     * transform).
     * @param value The value to move
     * @return The position the value moved from
     */
    int valueToFront(final byte value)
    {
        int index = 0;
        byte temp = mtf[0];
        if (value != temp)
        {
            mtf[0] = value;
            while (value != temp)
            {
                index++;
                final byte temp2 = temp;
                temp = mtf[index];
                mtf[index] = temp2;
            }
        }
        return index;
    }

    /**
     * Gets the value from a given index and moves it to the front of the MTF
     * list (inverse Move To Front transform).
     * @param index The index to move
     * @return The value at the given index
     */
    byte indexToFront(final int index)
    {
        final byte value = mtf[index];
        System.arraycopy(mtf, 0, mtf, 1, index);
        mtf[0] = value;

        return value;
    }
}
